Somchai Srisutthiyakorn, a former election commissioner, says he will join the Democrat party.
He did not say whether he would run as an MP candidate of the country’s oldest party, just that he would apply as a member.
Mr Somchai, who was sacked by Gen Prayut Chan-o-cha early this year, made the announcement on Saturday.
In a Facebook post, he thanked “friends” from 7-8 parties who had asked him to join them.
“All of these parties are pro-democracy. If they don’t support democracy, they won’t run in the poll,” he wrote.
Since the law allows a person to be member of only one party, Mr Somchai said he had to choose.
“I can’t pick the best party in the eye of everyone. That’s impossible, given each has different perceptions and values. But how do I choose so people will benefit the most in my view? The answer to this led to the final decision.
“On Sunday, I’ll apply to become a member of the Democrat party,” he concluded.
On Thursday, he wrote he would join a party and one of his criteria is that it must not support dictatorship.
After leaving the Election Commission (EC), Mr Somchai has been acting dean of the School of Political Science and Laws at Walailak University in Nakhon Si Thammarat province.
Earlier in his career, he was a lecturer and later deputy dean at Thammasat University’s Faculty of Political Science. After that, he was instrumental in a number of election monitoring groups including the Open Forum for Democracy (P-NET).
He was chosen an EC commissioner in 2014. In March this year, Gen Prayut, as chief of the the National Council for Peace and Order, sacked him by his authority under Section 44 of the interim constitution, citing as reasons “inappropriate behaviours” involving his comments on the coming election and a conflict of interest after he applied to be EC secretary-general without first resigning as a commissioner.